Friction stir welding is a relatively new process using a rotating tool to join two workpieces in a solid state. For example, such a process is described in U.S. Pat. No. 5,460,317 to Thomas et al., the contents of which are hereby incorporated by reference in its entirety. When using friction stir welding to join two workpieces, or repair cracks in a single workpiece, one of the primary parameters that typically must be monitored and controlled is the force exerted by the tool on the workpieces or workpiece. The magnitude of the force exerted by the tool must be maintained above a prescribed minimum in order to generate the required frictional heating of the workpieces. When linearly joining two workpieces, the tool is typically plunged by the friction stir welding machine to a depth necessary to produce the required force to generate the frictional heating. Once that force is achieved, it is continuously monitored to ensure sufficient force is maintained.
Whereas conventional systems for performing friction stir welding can adequately join workpieces or repair cracks in a single workpiece, such systems have drawbacks. In this regard, conventional systems are typically comprised of costly, dedicated machinery for performing friction stir welding. More particularly, as the force exerted by the tool on the workpiece(s) is one of the primary parameters that typically must be monitored and controlled when using friction stir welding, conventional systems for performing friction stir welding typically require a dedicated means for measuring such force. For example, conventional systems typically require devices such as strain gauge load cells, piezoelectric load cells, dynamometers, pneumatic load cells and/or hydraulic load cells to measure the force generated by the tool on the workpiece(s). And in the absence of such dedicated means for measuring force, conventional systems require a means for position control to control the force exerted by the tool on the workpiece(s). More particularly, other conventional systems require a means for controlling the position of the tool with respect to the workpiece(s) thereby assuming proper force is exerted by the tool.
In addition to the foregoing drawback, such conventional systems typically include costly machines dedicated to friction stir welding operations. In this regard, many times such machines may have significant downtime between friction stir welding operations, which further reduces manufacturing efficiency, and decreases flexibility of the machines used for manufacturing.